A quantitative and qualitative cytochemical study on human round-headed spermatozoa chromatin(Feulgen-DNA content, basic clear protein content, acid-resistance degree of DNP) was carried out. Feulgen-DNA and basic nuclear protein contents showed in different nuclear classes of various sizes within the whole population a variability of behaviour. Our data suggest the occurrence of meiotic malsegregation events followed by production of aneuploid gametes whose chromatin appears to be more compacted than controls.